Significant Effect of Rh on the h-BN-Supported Ni Catalyst for Dry Reformation of CH4: Insights from Density Functional Theory and Microkinetic Analysis

Abstract

The design of a catalyst by managing catalytic sites on an atomic scale is significant for tuning catalytic performance and offering high activity and selectivity for dry reforming of methane (DRM). We report a synergy effect of two sets of active sites (Ni and Rh) anchored on the surface hexagonal boron anitride nanosheets(h-BN), the whole reaction mechanism of DRM, as well as the competition processes over h-BN sheet-supported Ni-Rh catalysts (labeled as Ni9/h-BN and Ni8Rh1/h-BN) were studied by density functional theory calculations and microkinetic model analysis in the present work. Our present results show that the stability of hydrocarbon species like CHx(x = 1–4) on the Ni8Rh1/h-BN is significantly lower than that of Ni9/h-BN because of less electron transfer, and thus, strong carbon deposition resistance would be expected after the addition of Rh from the perspective of thermodynamics. CO2 activation is more efficient than that of CH4, and both CH4 and CO2 activation on Ni8Rh1/h-BN is more facile than that of pure Ni9/h-BN, and thus, higher catalytic activity of DRM can be expected on Ni8Rh1/h-BN. CO2 tends to decompose directly on both surfaces, and it was also found that O* is the main oxidizing agent for CH* intermediates and through the CH–O oxidation mechanism. Compared with the Ni9/h-BN surface, the selectivity of the DRM reaction is better on the Ni8Rh1/h-BN surface, and the ratio of H2/CO is close to one on the Ni8Rh1/h-BN surface based on the microkinetic model analysis. The microkinetic model result also shows that coke is difficult to form on the surface of Ni8Rh1/h-BN under experimental conditions. These synergistic effects of the two sets of atom sites on the same surface demonstrated a new method for designing a catalyst with high selectivity and stability for DRM.